Disc Cutter for an Earth Boring System

ABSTRACT

In one aspect of the present invention a disc cutter for an earth boring system includes an axle and a sintered polycrystalline ceramic disc disposed about and forming a continuous perimeter around the axle. The disc cutter may be attached to a drill bit comprising a body, working face and plurality of blades. 
     Another aspect of the present invention comprises a method of forming a disc cutter including providing a can of a generally cylindrical shape with a central axis, positioning a column of disposable material, carbide, and crystalline grains in such a manner so when put under high temperature and high pressure a compact in the shape of a disc cutter may be formed and a column from the center axis may be removed. Another method for forming a disc cutter comprises forming a plurality of compacts and bonding the compacts together in a generally toroidal shape.

BACKGROUND OF THE INVENTION

There exists a variety of rock boring machines used to cut through rock formations. Some machines such as the tunnel boring machine (TBM) may contain disc cutters. Disc cutters are generally rotatable around an axis and contain a continuous cutting surface. The prior art discloses rock boring machines containing said disc cutters.

One such disc cutter is disclosed in U.S. Pat. No. 6,131,676 to Friant et al., which is herein incorporated by reference for all that it contains. Friant et al. discloses small diameter rotary drill bits using rolling disc cutters. Novel small diameter rotary drill bits with detachable pedestal mounted rolling disc cutters are provided. The bit body has a plurality of longitudinal edge mounting slots located at preselected angularly spaced apart locations. Preferable, the slots each have an upper protective ledge and downwardly extending sidewalls. A set of peripheral pedestal mounts each having a mounting portion sized and shaped to fit into a preselected mounting slot are provided and each is detachably mounted in its preselected mounting slot. In one embodiment, the longitudinally extending slots further comprise a wedge shaped edge portion, and the pedestal mounts have a complimentary angularly shaped portion, so that when the pedestal mount is brought into a close fitting relationship with the longitudinal slot, the pedestal mount and the longitudinal slot are tightly and securely interfitting. The pedestal mounts each include, at the lower reaches thereof, at least one small diameter single cutting edge rolling disc cutter. The rolling disc cutters are affixed at individually preselected radially spaced apart locations with respect to a central longitudinal axis forming the center of rotation of the rotary drill bit. Also, each of the rolling disc cutters is mounted at a preselected angle delta with respect to the central longitudinal axis forming the center of rotation of the rotary drill bit. Also, the rolling disc cutters are preferable detachably affixed to the pedestal mounts.

Another such disc cutter is disclosed in U.S. Pat. No. 3,981,370 to Bingham et al., which is herein incorporated by reference for all that it contains. Bingham et al. discloses a rock-boring machine of the type comprising a rotatable headplate having a plurality of disc cutting units mounted on the front face of the headplate. Each disc cutting unit includes an annular rotatable body having a continuous recess extending around its periphery and a plurality of cutting segments located in the recess. The segments are secured in the recess by means of removable clamping means.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the present invention a disc cutter for an earth boring system comprises an axle and a sintered polycrystalline ceramic disc disposed about and forming a continuous perimeter around the axle.

The sintered polycrystalline ceramic disc may be comprised of a uniform polycrystalline ceramic material. The disc may contain a carbide core proximate the axle wherein a sintered polycrystalline ceramic external layer may be bonded to the carbide core. The carbide core may contain a polycrystalline ceramic interior layer proximate to the axle.

The sintered polycrystalline ceramic disc may contain grooves. The grooves may originate from a rim of the disc and terminate at the axle or may be continuous around the axle. The disc may also contain protrusions which extend from and add texture to the ceramic disc.

The sintered polycrystalline ceramic disc may contain two parallel cutting edges comprising supplemental internal angles or two parallel cutting edges each comprising an internal angle greater than 90 degrees with a rim comprising an internal angle measuring 80 to 140 degrees. The distance from at least one cutting edge to the core may be equal to the distance from the rim to the core.

The disc cutter may contain a plurality of sintered polycrystalline ceramic discs.

The axle may include a polycrystalline ceramic layer on its exterior surface.

In another aspect of the present invention a drill bit for penetrating earthen formations may include a body comprising of a working face. The working face may comprise a plurality of blades converging towards its center and diverging toward a gauge of the working face. An axle may be bonded to one of the plurality of blades. A sintered polycrystalline ceramic disc may be disposed about and forming a continuous perimeter around the axle.

The drill bit may also comprise at least one shear cutter disposed on one of the plurality of blades. The axle may be bonded to one of the plurality of blades at the gauge of the working face.

The sintered polycrystalline ceramic disc may be aligned tangent to a periphery of the working face or may be aligned perpendicular to the working face.

In another aspect of the present invention a method of forming a disc cutter comprises providing a first can which may be of a generally cylindrical shape and contain a central axis, positioning a first carbide substrate inside and coaxial with the first can, disposing crystalline grains inside the first can and forming a continuous perimeter around the first carbide substrate, applying high temperature and high pressure to the first can to form a first compact, and removing a column from the first compact along the central axis.

The first carbide substrate or the first can may comprise an axially hollow region wherein a disposable material may be disposed. The disposable material may be comprised of salt, silicon oxide, aluminum oxide, or tungsten carbide.

The column removed from the first compact may be removed by blasting, abrasive lapping, abrasive grinding, or electric discharge machining

A second can of a generally cylindrical shape and central axis may be provided and a column of disposable material may be positioned inside and coaxial with the second can. A second carbide substrate comprising a toroidal shape may be positioned inside the second can and encircling the second column. Crystalline grains may be disposed inside the second can and intermediate to the second carbide substrate and the column of disposable material. High temperature and high pressure may be applied to the second can to form a second compact. The first carbide substrate and the second carbide substrate may then be bonded together.

The first carbide substrate and the second carbide substrate may be bonded together by heating the first compact causing it to expand, depositing the second compact within the first compact, and cooling the first compact causing it to shrink onto the second compact.

In another aspect of the present invention a method of forming a disc cutter comprises providing a can which may be of a generally cylindrical shape and contain a central axis, positioning a column of disposable material along the axis of the can, positioning a carbide substrate which may be of a toroidal shape coaxial with the can and encircling the column, disposing crystalline grains inside the can and intermediate to the carbide substrate and column of disposable material, disposing crystalline grains inside the can and forming a continuous perimeter around the carbide substrate, applying high temperature and high pressure to the can to form a compact and removing the column from the compact.

In another aspect of the present invention a method of forming a disc cutter includes providing a can, disposing crystalline grains inside the can, positioning a carbide substrate adjacent to the crystalline grains, and applying high temperature and high pressure to the can to form a compact. The preceding steps may be repeated to form a plurality of compacts and wherein the compacts may be bonded together.

The compacts may be bonded together by brazing the carbide substrates of each compact. The sintered polycrystalline ceramic external layers of the compacts may be flush with each other after brazing. The compacts may be bonded so that they form a generally cylindrical shape. The generally cylindrical shape may be axially hollow, or a column from the center may be removed from the bonded compacts. The column may be removed by blasting, abrasive lapping, abrasive grinding, or electric discharge machining.

The can may be of a generally annular sector shape which may be formed by pressing the can around the carbide substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway view of an embodiment of a drilling operation.

FIG. 2 is a perspective view of an embodiment of a downhole drill bit.

FIG. 3 is a perspective view of an embodiment of a disc cutter.

FIG. 4 a is a cross-sectional view an embodiment of a disc cutter.

FIG. 4 b is a cross-sectional view of another embodiment of a disc cutter.

FIG. 5 a is a perspective view of an embodiment of a disc cutter.

FIG. 5 b is a perspective view of another embodiment of a disc cutter.

FIG. 6 a is a perspective view of an embodiment of a disc cutter.

FIG. 6 b is a perspective view of another embodiment of a disc cutter.

FIG. 6 c is a perspective view of another embodiment of a disc cutter.

FIG. 7 is a perspective view of an embodiment of a disc cutter.

FIG. 8 a is a perspective view of an embodiment of a disc cutter.

FIG. 8 b is a perspective view of another embodiment of a disc cutter.

FIG. 9 is a perspective view of an embodiment of a downhole drill bit.

FIG. 10 is a perspective view of an embodiment of a downhole drill bit.

FIG. 11 a is a plurality of longitudinal sections representing a method of forming a disc cutter.

FIG. 11 b is a flow chart of the steps in a method of forming a disc cutter.

FIG. 12 a is a perspective diagram of an embodiment depicting a method of subjecting a center column to the electrode of an electric discharge machine (EDM).

FIG. 12 b is a perspective diagram of an embodiment depicting a method of cutting a center column using an EDM wire.

FIG. 13 a is a plurality of longitudinal sections representing a method of forming a disc cutter.

FIG. 13 b is a flow chart of the steps in a method of forming a disc cutter.

FIG. 14 is a perspective view of an embodiment of a can.

FIG. 15 a is a plurality of longitudinal sections representing a method of forming a disc cutter.

FIG. 15 b is a flow chart of the steps in a method of forming a disc cutter.

FIG. 16 a is a plurality of longitudinal sections representing a method of bonding two substrates together.

FIG. 16 b is a flow chart of the steps in a method of bonding two substrates together.

FIG. 17 a is a plurality of longitudinal sections representing a method of forming a disc cutter.

FIG. 17 b is a flow chart of the steps in a method of forming a disc cutter.

FIG. 18 a is a plurality of longitudinal sections representing a method of forming a disc cutter.

FIG. 18 b is a flow chart of the steps in a method of forming a disc cutter.

FIG. 19 is a perspective view of an embodiment of a can.

FIG. 20 a is a plurality of longitudinal sections representing a method of bonding two substrates together.

FIG. 20 b is a flow chart of the steps in a method of bonding two substrates together.

FIG. 21 a is a plurality of longitudinal sections representing a method of forming a disc cutter.

FIG. 21 b is a flow chart of the steps in a method of forming a disc cutter.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT

Referring now to the figures, FIG. 1 discloses an embodiment of a drilling operation comprising a drilling derrick 101 supporting a drill string 100 inside a borehole 103. The drill string 100 comprises a drilling assembly 102 with a drill bit 104. The drilling assembly 102 may comprise electronic equipment able to send signals through a data communication system in the drill string 100 to a computer or data logging system 106 located at the surface.

FIG. 2 discloses an embodiment of a drill bit 104 comprising a body 201 and a working face 202. The working face 202 may comprise a plurality of blades 203 which may converge towards a center 204 of the working face 202 and diverge towards a gauge 205 of the working face 202. The drill bit 104 may comprise a disc cutter 206 comprising a sintered polycrystalline ceramic disc 207 disposed about and forming a continuous perimeter around an axle 208. The disc cutter 206 may be disposed in a hole 210 on the drill bit 104 such that the hole 210 may comprise bearing surfaces to slide against the disc cutter 206 and maintain the position of the disc cutter 206 on the axle 208. In this embodiment, the sintered polycrystalline ceramic disc 207 of the disc cutter 206 is aligned perpendicular to the working face 202.

FIG. 3 discloses an embodiment of a disc cutter 206 containing an axle 208 and a sintered polycrystalline ceramic disc 207 which may be disposed about and the axle 208. The sintered polycrystalline ceramic disc 207 contains a continuous perimeter 301 around the axle 208 such that cutting radius of the disc 207 may be the same as the radius of the disc cutter 206. In this figure, the sintered polycrystalline ceramic disc 207 may be composed of a uniform polycrystalline ceramic material. It is believed that the uniformity of the material eliminates weak areas from forming in the disc 207. The life of the disc cutter 206 may thus be extended during normal drilling operations.

FIG. 4 a discloses a cross sectional view of an embodiment of a disc cutter 206. The axle 208 acts as a central axis on which the sintered polycrystalline ceramic disc 207 can rotate. The axle 208 may comprise a polycrystalline ceramic layer 401 disposed on its exterior surface. The sintered polycrystalline ceramic disc 207 and the polycrystalline ceramic layer 401 may create a plain bearing. The sintered polycrystalline ceramic disc 207 and polycrystalline ceramic layer 401 may rub against each other without a sealing or lubricant. It is believed that this bearing extends the life of the disc cutter 206. In prior art disc cutters a bearing with a sealing has been necessary due to the materials used. However, abrasive substances may penetrate the sealing causing the sealing to deteriorate causing the need for the disc cutter to be replaced.

Also in FIG. 4 a, the axle 208 may comprise a first stopper 215 and a second stopper 216. The first stopper 215 may create an increased diameter on a portion of the axle 208. The second stopper 216 may comprise a ring such as a snap ring disposed around the axle 208. The first stopper 215 and the second stopper 216 may comprise bearing surfaces to slide against the disc cutter 206 and maintain the position of the disc cutter 206 on the axle 208.

FIG. 4 b discloses a cross sectional view of another embodiment of a disc cutter 206. In this figure, the sintered polycrystalline ceramic disc 207 may comprise a carbide core 402 proximate the axle 208. The carbide core 402 may comprise a polycrystalline ceramic interior layer 406 proximate the axle 208. The axle 208 may comprise a polycrystalline ceramic layer 401 disposed on its exterior surface. The polycrystalline ceramic interior layer 406 of the carbide bore 402 and the polycrystalline ceramic layer 401 on exterior surface of the axle 208 may create a bearing like that described previously.

A sintered polycrystalline ceramic external layer 403 may be bonded to the carbide core 402. The sintered polycrystalline ceramic external layer 403 may comprise polycrystalline diamond, synthetic diamond, vapor deposited diamond, silicon bonded diamond, cobalt bonded diamond, thermally stable diamond, polycrystalline diamond with a binder concentration of 1 to 40 weight percent, infiltrated diamond, layered diamond, monolithic diamond, polished diamond, course diamond, fine diamond, cubic boron nitride, diamond impregnated matrix, diamond impregnated carbide, silicon carbide, metal catalyzed diamond, or combinations thereof. It is believed that cubic boron nitride's metallic properties and heat tolerance make it a particularly effective external layer in certain formations.

Also in FIG. 4 b, the sintered polycrystalline ceramic disc 207 comprises a rim 404 comprising an internal angle 407 measuring 80 to 140 degrees located between two parallel cutting edges 405 each comprising an internal angle 408 greater than 90 degrees. The two parallel cutting edges 405 may allow for side loading. The two parallel cutting edges 405 may be significant because they may increase the cutting area of the disc cutter 206.

The rim 404 and the two parallel cutting edges 405 can be susceptible to breaking off during drilling operations. To minimize the likelihood of breaking off, the distance 409 from at least one parallel cutting edge 405 to the carbide core 402 may be equal to the distance 410 from the rim 404 to the carbide core 402.

FIG. 5 a discloses a perspective view of a disc cutter 400. The disc cutter 400 may contain a sintered polycrystalline ceramic disc 207 comprised of a rim 404 located between two parallel cutting edges 405.

FIG. 5 b discloses an embodiment of a disc cutter 501 containing a sintered polycrystalline ceramic disc 502 comprising two parallel cutting edges 503 comprising supplemental internal angles 504. This figure presents a disc cutter 501 which may be valuable in cases where only side loading is present.

FIG. 6 a discloses an embodiment of a disc cutter 601 containing grooves 604. Grooves 604 may be beneficial in downhole drilling by increasing the productivity and life of a disc cutter 601. During downhole operations, occasionally a disc cutter begins to slide along the earthen formation instead of cutting into it. This may put great wear on and could even break the disc cutter. The grooves 604 in the present embodiment may act like tread and grip into an earthen formation disallowing sliding. Grooves 604 can appear in a disc cutter 601 in a variety of patterns. In the embodiment shown, the grooves 604 originate at a rim 605 of the sintered polycrystalline ceramic disc 606 and terminate at an axle 607.

FIG. 6 b discloses another embodiment of a disc cutter 602 containing grooves 608. In this embodiment the grooves 608 are continuous around an axle 609.

FIG. 6 c discloses an embodiment of a disc cutter 603 containing protrusions 610 which may extend from and add texture to a sintered polycrystalline ceramic disc 612. The protrusions 610 may increase productivity and life of a disc cutter by preventing the disc cutter from sliding. Protrusions 610 can appear on a disc cutter in a variety of patterns. In this figure, the protrusions 610 originate at a rim 611 of the sintered polycrystalline ceramic disc 612 and terminate at an axle 613.

FIG. 7 discloses an embodiment of a disc cutter 701 comprising a plurality of sintered polycrystalline ceramic discs 702 disposed about an axle 705. The plurality of discs 702 may increase the cutting area of the disc cuter 701. Each disc 702 may be composed of a uniform polycrystalline ceramic material and comprise a continuous perimeter 703.

FIG. 8 a discloses an embodiment of a disc cutter 801. The disc cutter 801 comprises a sintered polycrystalline ceramic disc 802 which may be disposed about and form a continuous perimeter 804 around an axle 803. In this embodiment, the ceramic disc 802 is freely rotatable about the axle 803.

FIG. 8 b discloses an embodiment of a disc cutter 805. The disc cutter 805 comprises a sintered polycrystalline ceramic disc 806 which may be disposed about and form a continuous perimeter 808 around an axle 807. In this embodiment, the ceramic disc 805 is fixed to the axle 807 such that the ceramic disc 805 and the axle 807 rotate together.

FIG. 9 discloses another embodiment of a drill bit 901 comprising a body 910 and a working face 905. In the embodiment shown, the drill bit 901 contains a disc cutter 902 comprising a sintered polycrystalline ceramic disc 903 disposed about and forming a continuous perimeter around an axle 904. The sintered polycrystalline ceramic disk 903 may be aligned tangent to the periphery of the working face 905. The drill bit 901 may also contain at least on shear cutter 906 disposed on one of the plurality of blades 907. During the drilling process, the at least one shear cutter 906 and disc cutter 902 may serve different functions. The combination of using both types of cutters may be superior over using only one type in certain conditions.

FIG. 10 discloses another embodiment of a drill bit 1001 comprising a body 1010 and a working face 1007. In this figure, the drill bit 1001 contains a disc cutter 1002 comprising a sintered polycrystalline ceramic disc 1003 disposed about and forming a continuous perimeter around an axle 1004. The sintered polycrystalline ceramic disc 1003 may be bonded to one of the plurality of blades 1005 at a gauge 1006 of the working face 1007. A disc cutter 1002 located in this position may enlarge the area in which the drill bit 1001 is drilling. This embodiment may also include a covering 1015 which may be placed over the axle 1004. The covering 1015 may prevent the axle 1004 from coming loose during normal drilling operations. The covering 1015 may comprise bearing surfaces to slide against the disc cutter 1002 and maintain the position of the disc cutter 1002 on the axle 1004.

FIG. 11 a discloses steps in a method of forming a disc cutter comprising a sintered polycrystalline ceramic external layer 1108 and a carbide core 1109. A can 1101 comprising a generally cylindrical shape and a central axis may be provided. A carbide substrate 1102 may be positioned inside and coaxial with the can 1101. Crystalline grains 1103 may be disposed inside the can 1101 and form a continuous perimeter around the carbide substrate 1102. High temperature 1104 and high pressure 1105 may be applied to the can 1101 to form a compact 1106 comprising a sintered polycrystalline ceramic external layer 1108. A column 1107 of carbide substrate 1102 may be removed from the compact 1106 along the central axis thus forming a compact 1106 of a generally toroidal shape. The compact 1106 may be used as a disc cutter comprising a sintered polycrystalline ceramic external layer 1108 and a carbide core 1109 with the insertion of an axle.

FIG. 11 b discloses a flow chart of the steps in a method of forming a disc cutter which correspond to the longitudinal sections in FIG. 11 a.

FIG. 12 a discloses a first step of removing the column 1107 from the compact 1106 along the central axis as described previously. An electrode 1201 of an electric discharge machine (EDM) may be plunged into the carbide substrate 1102 of the compact 1106 forming an initial cavity.

FIG. 12 b discloses a second step of removing the column 1107 from the compact 1106. After the penetration by the EDM, an EDM wire 1202 may be threaded through the initial cavity. The EDM wire 1202 may clean the initial cavity of excess material forming a hollow column in the compact 1106.

FIG. 13 a discloses steps in a method of forming a disc cutter comprising a sintered polycrystalline ceramic external layer 1308 and a carbide core 1309. A can 1301 comprising a generally cylindrical shape and a central axis may be provided. A column of disposable material 1302 may be positioned inside and coaxial with the can 1301. The column of disposable material 1302 may comprise salt, silicon oxide, aluminum oxide or tungsten carbide. A carbide substrate 1303 comprising an axially hollow region may be positioned inside the can 1301 and around the column of disposable material 1302. Crystalline grains 1304 may be disposed inside the can 1301 and form a continuous perimeter around the carbide substrate 1303. High temperature 1305 and high pressure 1306 may then be applied to the can 1301 to form a compact 1307 comprising a sintered polycrystalline ceramic external layer 1308. The column of disposable material 1302 may then be removed from the compact 1307. The compact 1307 may be used as a disc cutter comprising a sintered polycrystalline ceramic external layer 1308 and a carbide core 1309 with the insertion of an axle.

FIG. 13 b discloses a flow chart of the steps in a method of forming a disc cutter which correspond to the longitudinal sections in FIG. 13 a.

FIG. 14 discloses a can 1401 used in a method of forming a disc cutter. The can 1401 comprises a generally cylindrical shape comprising an axially hollow region 1402. The can 1401 could be used in a method similar to that shown in FIGS. 13 a and 13 b. When high temperature and high pressure is applied to the can 1401, a disposable material may be disposed within the axially hollow region 1402. The disposable material would prevent the can 1401 from collapsing inward under the extreme conditions.

FIG. 15 a discloses steps in a method of forming a disc cutter comprising a polycrystalline ceramic interior layer 1508, carbide core 1509, and a sintered polycrystalline ceramic external layer 1510. A can 1501 comprising a generally cylindrical shape and a central axis may be provided. A column of disposable material 1502 may be positioned inside and coaxial with the can 1501. A carbide substrate 1503 comprising a toroidal shape may be positioned coaxial with the can 1501 and encircling the column 1502. Crystalline grains 1504 may be disposed inside the can 1501 intermediate to the carbide substrate 1503 and the column of disposable material 1502. High temperature 1505 and high pressure 1506 may be applied to the can 1501 to form a compact 1507 comprising a polycrystalline ceramic interior layer 1508. The column of disposable material 1502 may be removed from the compact 1507. The carbide substrate 1503 of compact 1507 may be bonded to the carbide substrate 1102 of compact 1106. The carbide substrate 1503 and carbide substrate 1102 may become the carbide core 1509 when bonded together. The compact 1507 may be used as a disc cutter comprising a sintered polycrystalline ceramic external layer 1510 and carbide core 1509 with the insertion of an axle. A plain bearing may be formed when the polycrystalline ceramic interior layer 1508 is combined with an axle comprised of a polycrystalline ceramic exterior surface.

FIG. 15 b discloses a flow chart of the steps in a method of forming a disc cutter which correspond to the longitudinal sections in FIG. 15 a.

FIG. 16 a discloses steps in a method of bonding the carbide substrate 1503 of compact 1507 to the carbide substrate 1102 of compact 1106. Heat 1601 may be applied to the compact 1106 causing it to expand. The compact 1507 may be deposited within the compact 1106. The compact 1106 may then be cooled 1602 causing it to shrink. The compact 1106 and the compact 1507 may be bonded together as the compact 1106 shrinks with the compact 1507 deposited within it.

FIG. 16 b discloses a flow chart of the steps in a method of bonding two substrates together which correspond to the longitudinal sections in FIG. 16 a.

FIG. 17 a discloses steps in a method of forming a disc cutter comprising a polycrystalline ceramic interior layer 1709, carbide core 1710, and a sintered polycrystalline ceramic external layer 1711. A can 1701 comprising a generally cylindrical shape and a central axis may be provided. A column of disposable material 1702 may be positioned inside and coaxial with the can 1701. A carbide substrate 1703 comprising a toroidal shape may be positioned inside and coaxial with the can 1701 and encircling the column of disposable material 1702. Crystalline grains 1704 may be disposed inside the can 1701 and intermediate the carbide substrate 1703 and column of disposable material 1702. Crystalline grains 1705 may be disposed inside the can and forming a continuous perimeter around the carbide substrate 1703. High temperature 1706 and high pressure 1707 may be applied to the can 1701 forming a compact 1708 comprising a carbide core 1710, and a sintered polycrystalline ceramic external layer 1711. The column of disposable material 1702 may be removed from the compact 1708. The compact 1708 may be used as a disc cutter comprising a sintered polycrystalline ceramic external layer 1711, carbide core 1710 and polycrystalline ceramic interior layer 1709 with the insertion of an axle. A plain bearing may be formed when the polycrystalline ceramic interior layer 1709 is combined with an axle comprised of a polycrystalline ceramic exterior surface.

FIG. 17 b discloses a flow chart of the steps in a method of forming a disc cutter which correspond to the longitudinal sections in FIG. 17 a.

FIG. 18 a discloses a method of forming a disc cutter comprising a carbide core 1808 and a sintered polycrystalline ceramic external layer 1809. A can 1800 may be provided. Crystalline grains 1801 may be disposed inside the can 1800. A carbide substrate 1802 may be positioned inside the can 1800 and adjacent to the crystalline grains 1801. High temperature 1803 and high pressure 1804 may be applied to the can 1800 forming a compact 1805. The preceding steps may then be repeated forming a plurality of compacts 1805. The plurality of compacts 1805 may be bonded together such that they form an axially hollow generally cylindrical shape 1806 comprising a hollow region 1807. An axle may be inserted into the hollow region 1807 such that a disc cutter comprising a carbide core 1808 and a sintered polycrystalline ceramic external layer 1809 carbide core 1808 and a sintered polycrystalline ceramic external layer 1809 is formed.

FIG. 18 b discloses a flow chart of the steps in a method of forming a disc cutter which correspond to the longitudinal sections in FIG. 18 a.

FIG. 19 discloses the can 1901 comprising a generally annular sector shape. The can 1901 may originally be a can 1901 of generally rectangular shape but may be formed by pressing 1902 the can 1901 around the carbide substrate 1803. The can 1901 comprises a narrow opening 1904 such that the carbide substrate 1803 cannot fit through the narrow opening 1904 and fill the volume of the can 1901. The carbide substrate 1803 may fit through the opening 1905 of the can 1901 wherein the can 1901 may be pressed 1902 together around the carbide substrate 1803. The shape of the can 1901 allows a plurality of compacts to be bonded together in an axially hollow generally cylindrical shape.

FIG. 20 a discloses steps in a method of bonding the carbide substrate 2001 of the compact 2002 to the carbide substrate 2003 of the compact 2004. A braze metal 2005 may be positioned intermediate the carbide substrate 2001 and the carbide substrate 2003. The carbide substrate 2001, carbide substrate 2003 and braze metal 2005 may be heated 2010 until the braze metal 2005 melts. The melted braze metal 2005 may adhere to both the carbide substrate 2001 and carbide substrate 2003 and may be cooled 2011 to become a solid. As the metal braze 2005 is cooled, it acts as a glue between the carbide substrate 2001 and carbide substrate 2003 thus bonding them together. The compact 2002 may comprise a sintered polycrystalline ceramic external layer 2006 and the compact 2004 may comprise a sintered polycrystalline ceramic external layer 2007 wherein the ceramic external layer 2006 and ceramic external layer 2007 may be flush with each other after brazing.

FIG. 20 b discloses a flow chart of the steps in a method of bonding carbide substrates together which correspond to the longitudinal sections in FIG. 20 a.

FIG. 21 a discloses a method of forming a disc cutter comprising a carbide core 2108 and a sintered polycrystalline ceramic external layer 2109. In this figure, a can 2100 of a generally rectangular shape may be provided. Crystalline grains 2101 may be disposed inside the can 2100. A carbide substrate 2102 may be positioned inside the can 2100 and adjacent to the crystalline grains 2101. The can 2100 may be pressed 2110 to form a generally triangular shape comprising a curved base. High temperature 2103 and high pressure 2104 may be applied to the can 2100 forming a compact 2105. The preceding steps may be repeated forming a plurality of compacts 2105. The plurality of compacts 2105 may be bonded together such that they form a generally cylindrical shape 2106. A column may be removed from the center of the bonded compacts to form a hollow region 2107. The column may be removed by blasting, abrasive lapping, abrasive grinding, or electric discharge machining An axle may be inserted into the hollow region 2107 such that a disc cutter comprising a carbide core 2108 and a sintered polycrystalline ceramic external layer 2109 may be formed.

FIG. 21 b discloses a flow chart of the steps in a method of forming a disc cutter which correspond to the longitudinal sections in FIG. 21 a.

Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention. 

1. A disc cutter for an earth boring system, comprising: an axle; a sintered polycrystalline ceramic disc disposed about the axle; and the ceramic disc forming a continuous perimeter around the axle.
 2. The disc cutter of claim 1, wherein the axle comprises a polycrystalline ceramic layer disposed on an exterior surface of the axle.
 3. The disc cutter of claim 1, wherein the sintered polycrystalline ceramic disc is composed of a uniform polycrystalline ceramic material.
 4. The disc cutter of claim 1, wherein the sintered polycrystalline ceramic disc comprises a carbide core proximate the axle and a sintered polycrystalline ceramic external layer bonded to the carbide core.
 5. The disc cutter of claim 4, wherein the carbide core comprises a polycrystalline ceramic interior layer proximate the axle.
 6. The disc cutter of claim 1, wherein the sintered polycrystalline ceramic disc is freely rotatable about the axle
 7. The disc cutter of claim 1, wherein the sintered polycrystalline ceramic disc is fixed to the axle.
 8. The disc cutter of claim 1, wherein the sintered polycrystalline ceramic disc comprises grooves.
 9. The disc cutter of claim 8, wherein the grooves originate from a rim of the sintered polycrystalline ceramic disc and terminate at the axle.
 10. The disc cutter of claim 8, wherein the grooves are continuous around the axle.
 11. The disc cutter of claim 1, wherein the sintered polycrystalline ceramic disc comprises protrusions extending from and adding texture to the ceramic disc.
 12. The disc cutter of claim 1, wherein the sintered polycrystalline ceramic disc comprises two parallel cutting edges comprising supplemental internal angles.
 13. The disc cutter of claim 1, wherein the disc comprises a rim comprising an internal angle measuring 80 to 140 degrees between two parallel cutting edges each comprising an internal angle greater than 90 degrees.
 14. The disc cutter of claim 13, wherein the sintered polycrystalline ceramic disc comprises a carbide core and a distance from at least one cutting edge to the carbide core is equal to a distance from the rim to the carbide core.
 15. The disc cutter of claim 1, further comprising a plurality of sintered polycrystalline ceramic discs.
 16. A drill bit for penetrating earthen formations, comprising: a body comprising a working face; the working face comprising a plurality of blades converging toward a center of the working face and diverging toward a gauge of the working face; an axle bonded to one of the plurality of blades; and a sintered polycrystalline ceramic disc disposed about the axle and the disc forming a continuous perimeter around the axle.
 17. The drill bit of claim 16, further comprising at least one shear cutter disposed on one of the plurality of blades.
 18. The drill bit of claim 16, wherein the axle is bonded to one of the plurality of blades at the gauge of the working face.
 19. The drill bit of claim 16, wherein the sintered polycrystalline ceramic disc is aligned tangent to a periphery of the working face.
 20. The drill bit of claim 16, wherein the sintered polycrystalline ceramic disc is aligned perpendicular to the working face. 